Multicell Multiple Input Multiple Output (MIMO) techniques improve a sector throughput and a cell-edge throughput through co-channel interference cancellation, power gain, channel rank/condition advantage, Base Station (BS) macro diversity protection, and multi-BS collaborative precoding. The multicell MIMO techniques can be divided into open-loop (OL) multicell MIMO techniques and closed-loop (CL) multicell MIMO techniques.
Typically, two multicell MIMO schemes are considered. The first scheme is a single BS precoding technique (hereafter, referred to as a first multicell MIMO scheme) with multi-BS coordination, which includes Precoding Matrix Index (PMI) coordination, supported by a feedback-based codebook and interference nulling supported by the codebook based on the feedback or uplink sounding. When CL-MIMO precoding is applied to a serving cell and neighbor cells, the single BS precoding with the multi-BS coordination may be enabled by the BS for one or more Mobile Stations (MSs). Inter Cell Interference (ICI) may be mitigated by coordinating precoders applied to the neighbor cells, based on the feedback from the MSs to the respective serving BSs through the signaling of an upper layer. PMI coordination may be achieved by way of PMI restriction in which the serving BS suggests to use the PMI by informing the neighbor BSs of the PMI causing the interference, using the PMI fed back from the MS, or as PMI recommendation by recommending the PMI for use by informing the neighbor BSs of the PMI which mitigates the interference.
The second scheme is a Joint MIMO transmission across multiple BSs technique (hereafter, referred to as a second multicell MIMO scheme). The BS and the MS optionally support both adaptive precoding and non-adaptive precoding. The adaptive precoding is based on multi-BS joint processing such as CL-Macro Diversity (MD) and Collaborative (Co)-MIMO. When the adaptive precoding or the non-adaptive precoding is applied to the serving cell and the neighbor cells and user data is shared among the multiple cells, the multi-BS joint MIMO processing may be enabled by the BS for one or more MSs. Using the adaptive precoding, a precoder matrix Wk is generated from the feedback of the MS such as codebook and sounding channel. The two adaptive precodings based on the multi-BS joint processing support the CL-MD and the Co-MIMO. When the CL-MD is activated, a plurality of BSs conducts the joint MIMO transmission to one MS. When the Co-MIMO is activated, the multiple BSs conduct the joint MIMO transmission to a plurality of MSs through multi-user MIMO scheduling and precoding.
The first multicell MIMO scheme and the second multicell MIMO scheme as discussed above require a trigger mechanism design to optionally apply them according to a channel environment. When the trigger mechanism is not designed, many MSs moving in the cell edge need to feed back corresponding information such as Received Signal Strength Indicator (RSSI), Signal-Interference-plus-Noise Ratio (SINR), and PMI for the serving BS or an interference BS, Normalized Interference Power (NIP) of each interference BS, or interference power of the interference BS. In addition, each BS needs to carry out the complicated scheduling based on a lot of other feedback information.
In this respect, what is needed is a mechanism for efficiently triggering the multicell MIMO schemes in a multiple antenna system.